IC transfer device

ABSTRACT

An IC transfer device is provided that can combat the generation of the cracks in handling the IC packages. When the hand  3  comes in contact with the IC package  4  accommodated on the tray  5,  a load cell  6  comes in contact with a bottom surface of a base  10.  Reference values as to a press-down amount and a press-down speed of the hand  3  are set in a setting section so as not to cause cracks in the IC package  4  due to the instantaneous load at the time of contact between the hand  3  and the IC package  4.  In a transfer operation, when detecting the contact between the hand  3  and the IC package  4,  a control section  20  controls a servomotor of the hand drive mechanism  22  so that the hand  3  operates according to the reference values set in the setting section.

This application is a national stage entry of PCT/JP02/13549international Filing Date: Dec. 25, 2002.

1. Technical Field

The present invention generally relates to an IC transfer device thattransfers an IC package such as a QFP (Quad Flat Package), a BGA (BallGrid Package), a CSP (Chip Size Package), and a wafer-level CSP.

2. Background Art

In an electrical characteristic tester, a visual check machine, aburn-in tester and the like, the IC transfer device is used as a handlerfor picking and placing a target IC package in place or for displacingthe IC package.

As shown in FIG. 1, the IC package 4 is accommodated in a tray 5 beforebeing placed in the tester. The IC transfer device moves a hand 3downward toward the IC package 4 to pick up the IC package 4accommodated in the tray 5 and then transfers that IC package 4 to apredetermined place and then places it in the tester. A drive device formoving the hand 3 up or down is provided with the IC transfer device.For example, a drive mechanism, such as a servomotor for rotating a ballscrew, is provided to raise or lower the hand 3 vertically. After thehand 3 comes in contact with the IC package 4, the bottom surface of thehand 3 (i.e., the surface that makes contact with the IC package 4) isfurther lowered by a predetermined amount so as to apply pressure to theIC package 4 and thereby chuck the IC package 4.

A typical procedure for setting the IC transfer device is as follows. Asa first step, under conditions of the IC package 4 being on the tray 5,the height (stroke) of the hand 3 is adjusted appropriately so that thehand 3 can chuck the IC package 4. At this time, the height adjustedaccording to a setting for a thick-type QFP or BGA (about 3 mmthickness) transferred previously is often utilized. For the thick-typeQFP or BGA, the hand 3 is further lowered after making contact with thetop surface of the IC package 4 until the height of bottom surface ofthe hand 3 is about 2 mm lower than the top surface of the IC package 4so as to ensure the chuck operation. This lowering of the hand 3 aftermaking contact with the IC package 4 is referred to as “pressing down”.Inadequate chuck-operation causes the IC package to drop from the hand 3during a transferring process. For this reason, the “pressing down” iscarried out.

As long as the IC transfer device can transfer the IC package withoutproblems such as an chucking error, an error causing the device to stop,a deformation of a terminal of the IC package, and a deformation of theoutside shape of the IC package, the IC transfer device is considered tobe a device equipped with the capacity to transfer the IC package.

The lowering speed of the hand 3 when the hand 3 is lowered to pick upthe IC package is a significant factor on which operating efficiencydepends. With regard to the lowering speed, a number of IC transferdevices have been developed for an improved transferring speed to meetthe needs in the age of the thick-type QFP or BGA. The recent-model ICtransfer devices enable an index time for changing of the IC packages(i.e., the interval between each transferring of an IC package) to beless than 1 sec. Because a reduction of the lowering speed of the hand 3results in a reduction of the operating efficiency, a manufacturer'ssuggested lowering speed has been commonly employed.

When the hand 3 moves downward toward the top surface of the IC package4 and then further moves downward by a predetermined amount after itmakes contact with the top surface, the impact on the IC package 4 issignificant due to several factors such as weight of the hand 3, shapeof the hand 3, contact area between them, and speed of the hand 3. Theload exerted on the IC package 4 by the hand 3 can be divided into twotypes of load, that is to say, an impact load generated when the hand 3comes in contact with the IC package 4, and a static load generated whenthe hand 3 is pressed down after making contact with the IC package 4.The combination of these two types of load is referred to as aninstantaneous load.

Before this time, the instantaneous load has not been under control.However, if the instantaneous load is not taken into account in the useof the IC transfer device, significant quality problems will occur, suchas cracks in a chip inside the IC package (hereafter referred to as chipcracks), and cracks visible from the outside of the IC package, in thecase of a large instantaneous load. These problems are more likely tooccur in the case of a thin-type IC package (less than 1 mm thickness).

To maintain quality means to make the IC package free from any chipcracks. However, the chip cracks inside the IC package cannot bedetected by visual check or a visual inspection.

As the cracks show up as various forms of defects through the electricalcharacteristic test depending on their location, the cracks can bedetected. However, the chip cracks include the minute cracks that cannotbe visually detected. Unfortunately, there may be cases where the ICpackages with the minute cracks are considered to meet pass criteriaeven by the electrical characteristic test. Accordingly, one cannot saywith assuredness that all of the IC packages with the chip cracks arerejected as defective items through the electrical characteristic test.

By the way, the chip cracks generated by the electrical characteristictest process, as is the case with a prior and a subsequent process(i.e., a burn-in process or a visual check process), cannot be detected,unless an individual observation for every IC package is performedthrough use of a Scanning Acoustic Tomograph (SAT). However, the SAT ismade use of only at the beginning of the development of the IC packagefor a certificate test for examining the presence or absence of anexfoliation inside the IC package, so the SAT cannot be made use of at astage of volume production. Thus, there may be cases where the cracksinside the IC package or the minute cracks are overlooked at shipmentand result in later problems.

DISCLOSURE OF THE INVENTION

It is a general object of the present invention to provide an ICtransfer device that can avoid the generation of the cracks in the ICpackage during the handling of the IC package.

It is another object of the present invention to provide a method ofcontrolling such an IC transfer device.

To achieve the object, according to one aspect of the invention, the ICtransfer device comprises a hand for chucking an IC package on a tray; ahand drive mechanism for moving the hand downward toward the IC package;a control section for controlling the hand drive mechanism; a load cellwhich is arranged such as to come in contact with a component integratedwith the hand when the hand comes in contact with the IC package, andmeasures load applied thereto by a lowering operation of the hand; and asetting section for setting reference value as to the lowering operationof the hand, wherein the control section is configured to control thehand drive mechanism based on the reference value while monitoring anoutput of the load cell.

With this arrangement, by monitoring a peak value of the production ofthe load cell, it becomes possible to manage an instantaneous loadexerted instantaneously at impact on the IC package when the hand comesin contact with the IC package. Furthermore, by controlling the handdrive mechanism based on the reference value while continuouslymonitoring the instantaneous load, it becomes possible to transfer theIC package without producing the chip cracks therein. Consequently, itbecomes possible to save time required to diagnose the low productionyields of the IC package due to the chip cracks and guarantee highquality of the IC package after shipment.

Preferably, the reference value comprises a lowering speed of the handwhen the hand comes in contact with the IC package. With thisarrangement, it becomes possible to control the magnitude of aninstantaneous load exerted instantaneously at impact on the IC package.

The reference value may comprise not only a lowering speed but also apress-down amount and a press-down speed itself of the hand after makingcontact with the IC package.

The irregularities in the lowering operation may be detected bydetermining whether the peak value of the load cell exceeds apredetermined threshold value or not.

Preferably, the lowering speed of the hand before making contact withthe IC package is higher than that of the hand after making contact withthe IC package. With this arrangement, the operating efficiency of theIC transfer device can be increased.

Preferably, the hand drive mechanism comprises a servomotor or a stepmotor. With this arrangement, it becomes possible to control the handwith a high degree of precision.

Preferably, the hand has an end face suitable for holding the ICpackage, for example, by means of vacuum suction. With this arrangement,it becomes possible to expand the applicability of the present inventionto the traditional general purpose IC transfer device.

According to another aspect of the invention, a method of controlling ICtransfer device comprises moving a hand downward toward the IC packageon a tray; changing a lowering speed of the hand so that the hand comesin contact with the IC at a predetermined speed; monitoring an output ofa load cell at the time the hand comes in contact with the IC package,said load cell arranged such as to come in contact with a componentintegrated with the hand when the hand comes in contact with the ICpackage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a IC transfer device according to prior art.

FIG. 2 is a front view of a IC transfer device in a calibration mode.

FIG. 3 is a front view of a IC transfer device in an IC package-transfermode.

FIG. 4 is a block diagram for control of the hand according to thepresent invention.

FIG. 5 is a diagram illustrating the instantaneous load.

FIG. 6 is a flow chart according to the present invention for showingthe sequence of the operation for setting a reference value.

FIG. 7 is a flow chart according to the present invention for showingthe operation for transferring the IC package.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, principles and embodiments of the present inventionwill be described with reference to the accompanying drawings.

Example reference values set in a setting section 24 consist of apress-down amount and a press-down speed during the time a hand movesdown further and presses an IC package downward after making contactwith the IC package. Another example of reference values set in thesetting section 24 consists of the press-down amount during the handmoves down further and presses an IC package downward after makingcontact with the IC package, and an output of a load cell when the handcomes in contact with the IC package.

For the purpose of increased operating efficiency, a control section 22preferably controls a hand drive mechanism 20 so that a lowering speedof the hand before making contact with the IC package is higher than thepress-down speed after making contact with the IC package. In order toprecisely control the press-down operation, the hand drive mechanism 20for moving the hand vertically is preferably either a servomotor or astepping motor. One example of the hand is the one that is provided witha mechanism suitable for holding the IC package to its end surface.

[Embodiment]

FIGS. 2 and 3 show one embodiment of the present invention. FIG. 2illustrates an IC transfer device in a state of performing acalibration, and FIG. 3 illustrates the IC transfer device in a state oftransferring an IC package. In order to raise or lower a hand 3vertically, a base 10 on which the hand 3 is mounted is provided at thebottom of a ball screw 2, and a servomotor of the hand drive mechanism20 for rotating the ball screw 2 is provided. The ball screw 2 isrotatablely attached to the base 10. When the ball screw 2 is rotated bythe hand drive mechanism 20, the up-and-down movement of the ball screw2 causes the up-and-down movement of the base 10 without causing arotary movement of the base 10. The hand 3 has an end face suitable forholding the IC package 4 by means of vacuum suction and chucking itthereto.

The IC package 4 is accommodated on a tray 5, such as a shuttle, astage, a socket and a receptacle, from which the IC package 4 istransferred to a tester or other desired places. As shown in FIG. 2, aload cell 6 is provided to the position where it comes in contact withthe bottom surface of the base 10 when the end face of the hand 3, suchas a transfer hand, a collet, and a contactor, comes in contact with thetray 5. Alternately, as shown in FIG. 3, the load cell 6 is provided tothe position where it comes in contact with the bottom surface of thebase 10 when the end face of the hand 3 comes in contact with the ICpackage 4 accommodated on the tray 5. Although the base 10 is relativelylarge in size so as to facilitate the contact between the base 10 andthe load cell 6, the base 10 is not necessarily larger in size than atraditional base as far as it is capable of making contact with the loadcell 6. In order to make the height of the load cell 6 adjustable, theload cell 6 is secured to the top end of the ball screw 7 whose heightis adjustable by a drive mechanism 8 such as a servomotor.

The load cell 6 is provided with a strain gage therein, and a voltagegenerated by the strain gage as an output is sent to the control section22 of the hand drive mechanism 20. The impact load at the instant of thecontact between the end face of the hand 3 and the IC package 4 and thestatic load at the time of the subsequent pressing down are sent to thecontrol section 22 as an output of the load cell 6. Therefore, itbecomes possible to detect the instantaneous load exerted on the ICpackage 4. As shown in FIG. 4, the control section 22 stores thoseoutputs in a memory device which is incorporated into the settingsection 24 or provided separately from the control section 22.Alternatively, the setting section 24 may be incorporated into thecontrol section 22.

In a calibration mode for determining the reference position of the loadcell 6, as shown in FIG. 2, the tray not accommodating the IC package 4therein is prepared. Then, the hand 3 is lowered to the position wherethe end face of the hand 3 comes in contact with the tray 5. Thatposition of the hand 3 is determined as the reference position of thehand 3. While maintaining this condition, the position (height) of theload cell 6 is adjusted so that the load cell 6 makes contact with thebottom surface of the base 10. That position of the load cell 6 isdetermined as the reference position of the load cell 6.

In a transfer mode shown in FIG. 3 for transferring the IC package 4,thereference position is determined for every type of IC package based onthe reference position determined in the calibration mode. For example,in case of a thin-type IC package of 1 mm thickness, the position wherethe hand 3 comes in contact with the thin-type IC package is up 1 mmfrom the reference position. Likewise, the position of the load cell 6is adjusted by the servomotor up 1 mm from the reference positiondetermined in the calibration mode and then the load cell 6 is held inthat adjusted position.

It becomes possible to perform a measurement of the instantaneous loadat all times by setting the IC transfer device in the transfer modeshown in FIG. 3 and by recording a peak value of the measuredinstantaneous load at every transferring of the IC package 4. Inaddition to being capable of monitoring the instantaneous load, this ICtransfer device is capable of operating with the instantaneous loadwithin load specifications by feeding back the voltage of the straingage of the load cell 6 to the servomotor of the hand drive mechanism 20through a cable while continuously monitoring the instantaneous load.

Here, the load specifications define the magnitude of the load by whichthe chip cracks cannot be produced. Because the magnitude of theinstantaneous load that causes the chip cracks (i.e., potentiality ofthe chip cracks) varies from IC package to IC package, the magnitude ofload by which the chip cracks cannot be produced should be previouslydetermined at an evaluation stage. Although it is also possible to use apush-pull gage and the like for this evaluation, the IC transfer deviceaccording to the present embodiment can make this evaluation.Specifically, the hand 3 is lowered at the lowering speed of about 20mm/min under the control of the servomotor, and when the hand 3 comes incontact with the IC package 4, the gage readings of the load cell 6 istaken. This measurement is made for several samples of IC packages whilevarying the load (e.g., 1 kg for sample 1 and 2 kg for sample 2 and soon). An observation by SAT (Scanning Acoustic Tomograph) is carried outfor those samples to determine the critical load.

While the instantaneous load is a combination of the impact load and thestatic load, it is possible to detect these two types of load in turn.If these two types of load are managed respectively, it becomes possibleto control the impact load exerted initially on the IC package 4 bycontinuously monitoring the gage readings of the load cell 6, as in thisembodiment. However, it may be difficult to detect the static load,depending on the output of load cell 6 in a state of high-speedoperation of the IC transfer device. But the static load can be detectedbefore the IC package 4 is accommodated in the tray 5. So it is possibleto manage the static load as a daily check matter or a routine checkmatter at a setting of the production lots. Therefore, it is notnecessarily required to control the static load during the operation ofthe IC transfer device.

Furthermore, the static load is the load exerted finally between the endface of the hand 3 and the top surface of the IC package 4. Themagnitude of static load by which the chip cracks are produced issignificantly large (e.g., 10 kg). On the other hand, the impact loadcan yield the chip cracks, even if it is one-tenth of the static load(e.g., 1 kg). Accordingly, in terms of the present invention, it is notnecessary to manage the static load for every IC package 4 and aperiodic check is plenty good enough.

It is also possible to detect the impact load as well as the static loadat every transferring of the IC package 4, depending on the way of usingthe load cell 6. For example, the impact load as well as the static loadcan be detected, by upsizing the base 10 to which the hand 3 isattached, and by providing two load cells one on each side of the hand3. In this way, one of the load cells measures the impact load, whilethe other of the load cells measures the static load by keeping the hand3 in its lowermost position for a fixed period of time.

FIG. 5 shows the instantaneous load (i.e., the impact load and thestatic load) measured by the load cell 6 of the IC transfer deviceaccording to this embodiment. The impact load is generatedinstantaneously when the hand 3 comes in contact with the IC package andthe static load is generated when the hand 3 subsequently appliespressure to the IC package. In actual experiments, the instantaneousload was measured under several conditions. Especially important andadvantageous parameters among others are the press-down amount and thepress-down speed.

The press-down amount in the neighborhood of 2 mm is traditionally used,however, we set the parameters as follows. The press-down speed at theinstance when the hand 3 comes in contact with the IC package 4 was setto seventy percent of the limit of the lowering speed. The press-downamount was set to 0.1 mm, 0.4 mm, 0.7 mm, and 1.0 mm. The result of themeasurements is shown in the following Table 1.

TABLE 1 Press-down amount (speed = 70%) 0.1 mm 0.4 mm 0.7 mm 1.0 mmImpact load 0.43 kgf 0.78 kgf 0.95 kgf 1.39 kgf Static load 0.29 kgf0.32 kgf 0.47 kgf 0.74 kgfThe impact load increased from 0.43 kgf to 1.39 kgf as the press-downamount increased.

Then, the press-down speed was set to 60%, 70%, 80%, and 90% of thelimit of the lowering speed, with the press-down amount fixed at 0.4 mm(the press-down amount of 0.4 mm is the limit amount that cannot causethe transferring problems). The result of the measurements is shown inthe Table 2 below.

TABLE 2 Press-down speed (amount = 4 mm) 60% 70% 80% 90% Impact load0.41 kgf 0.77 kgf 0.96 kgf 1.36 kgf Static load 0.29 kgf 0.34 kgf 0.48kgf 0.74 kgfIn Table 2, the press-down speed is expressed as a percentage of thelimit of the lowering speed. Similarly, the load increased as press-downspeed increased. In this way, it becomes possible to reduce the impactload by controlling the lowering speed of the hand 3 immediately beforemaking contact with the IC package 4 and thereby the press-down speed ofthe hand 3. Furthermore, in a state of using the appropriate press-downamount and the press-down speed, it becomes possible to detectirregularities in the chuck operation by continuously monitoring theinstantaneous load.

FIG. 6 shows the operation for setting the reference values of a settingsection 24 shown in FIG. 4. First of all, an IC package as a sample isplaced on the tray 5, and then the sample is chucked by the hand 3 as aresult of driving the servomotor of the hand drive mechanism 20 based onthe predetermined press-down amount and the press-down speed. At thattime, the peak value of the load cell 6 is recorded. This peak valueindicates the instantaneous load.

Then, the chuck operation is repeated while changing the samples. Atevery chuck operation, the setting is changed according to thepress-down amount and the press-down speed predetermined for therespective sample. The peak values measured by the load cell 6 at everychuck operation are recorded. After the completion of the operationswith predetermined conditions, the observations by SAT for those samplesare carried out to determine the optimum value of the press-down amountand the press-down speed as well as the limit value of the instantaneousload based on the samples that have not experienced any cracks. Itshould be noted that while this embodiment comprises the use of thepress-down amount and the press-down speed as the reference values,other types of parameters, such as an output of the load cell (forexample, the peak value, or a calculated value of an impact energy), maybe used additionally or alternatively as a reference value.

FIG. 7 shows the actual operation for transferring the IC package 4after the completion of the setting of the reference values. Once theoperation is initiated and the servomotor is driven, the load iscontinuously monitored by use of the load cell 6. The control section 22controls the servomotor of the hand drive mechanism 20 so that thepress-down amount and the press-down speed conform to the referencevalues set in the setting section 24. For example, when the distancefrom the end face of hand 3 to the IC package 4 becomes a predeterminedthreshold value (for example, 2 mm), the control section 22 changes thelowering speed of the hand 3 so that the hand 3 comes in contact withthe IC package 4 at the speed of the reference value.

In the case of the reference values as to an output of the load cell,when the end face of hand 3 comes in contact with the IC package 4, thecontrol section 22 determines whether a peak value of the load cell 6exceeds a predetermined threshold value (the reference value set in thesetting section 24) or not. This determination enables the detection ofthe irregularities of the IC transfer device (for example, an error inadjustments or an error due to the environmental factors). After thehand 3 comes in contact with the IC package 4, the control section 22may controls the servomotor of the hand drive mechanism 20 so that thepress-down amount and the output of the load cell 6 conform to thereference values set in the setting section 24.

It should be noted that while this embodiment comprises the use of aservomotor as hand drive mechanism 20, other types of motors such as apulse motor are equally applicable.

Further, the present invention is not limited to these embodiments, andvariations and modifications may be made without departing from thescope of the present invention.

For example, the present invention is not limited to the hand forchucking the IC package on a tray, but is applicable to the hand forhandling the IC package when positioning, placing, or connecting the ICpackage with respect to a target such as a socket. In this case, thepressing down operation as mentioned above is carried out.

By the way, Japanese laid-open patent publication 2001-51018 disclosesan IC tester, in which the load cell is made use of to control the loadon the IC package. However, in this traditional IC tester, the load cellis made use of to monitor the contact pressure generated when acontactor is pressed against the IC package accommodated in measuringequipment (e.g., a socket) in order to guarantee the electric contactbetween a terminal of the IC package and a terminal of the socket,thereby stabilizing the electrical characteristic. However, in thistraditional IC tester, the instantaneous load at the instance a handcomes in contact with the IC package is not taken into account and onlythe measurement of the static load is performed. Although the load cellis made use of in the present invention, the present invention differsfrom these prior art cases especially in the aim and the way of usingthe load cell.

1. An IC transfer device comprising; a hand for chucking an IC packageon a tray; a hand drive mechanism for moving the hand downward towardthe IC package; a control section for controlling the hand drivemechanism; a load cell which is arranged such as to come in contact witha component integrated with the hand when the hand comes in contact withthe IC package, and measures load applied thereto by a loweringoperation of the hand; and a setting section for setting reference valueas to the lowering operation of the hand, wherein, the control sectionis configured to control the hand drive mechanism based on the referencevalue while monitoring an output of the load cell.
 2. The IC transferdevice according to claim 1, wherein, the reference value comprises alowering speed of the hand when the hand comes in contact with the ICpackage.
 3. The IC transfer device according to claim 2, wherein, thecontrol section changes the lowering speed of the hand so that the handcomes in contact with the IC at the speed of the reference value.
 4. TheIC transfer device according to claim 2, wherein, the reference valuefurther comprises a press-down amount and a press-down speed at the timethe hand is further lowered to be pressed down on the IC package aftermaking contact with the IC package.
 5. The IC transfer device accordingto claim 2, wherein, the reference value further comprises a press-downamount and the output of the load cell during the hand is furtherlowered to be pressed down on the IC package after making contact withthe IC package.
 6. The IC transfer device according to claim 2, wherein,the reference value as to lowering speed of the hand is less than thelowering speed of the hand before making contact with the IC package. 7.The IC transfer device according to claim 1, wherein, the controlsection detects irregularities in the lowering operation if a peak valueof the output of the load cell exceeds a predetermined threshold value.8. The IC transfer device according to claim 7, wherein, thepredetermined threshold value is determined so as not to cause cracks inthe IC package.
 9. The IC transfer device according to claim 1, wherein,the hand drive mechanism for moving the hand comprises a servomotor or astep motor.
 10. The IC transfer device according to claim 1, wherein,the hand is provided with a mechanism on its end face suitable forholding the IC package.
 11. An IC transfer device comprising; a handconfigured such as to hold an IC package; a hand drive mechanism formoving the hand with the IC package downward toward a target; a controlsection for controlling the hand drive mechanism; a load cell which isarranged such as to come in contact with a component integrated with thehand when the IC package comes in contact with the target, and measuresload applied thereto by a lowering operation of the hand; and a settingsection for setting reference values as to the lowering operation of thehand, wherein, the control section is configured to control the handdrive mechanism based on the reference value while monitoring an outputof the load cell.
 12. A method of controlling IC transfer devicecomprising the steps of; moving a hand downward toward the IC package ona tray; changing a lowering speed of the hand so that the hand comes incontact with the IC at a predetermined speed; monitoring an output of aload cell at the time the hand comes in contact with the IC package,said load cell arranged such as to come in contact with a componentintegrated with the hand when the hand comes in contact with the ICpackage.